1. Field of the Invention
This invention relates to ammonia analysis, and more particularly to a method for determining ammonia concentration with a microbial electrode electrochemically.
2. Description of the Prior Art
Recently, it has been said that ammonia, one of the members of a nitrogen cycle in nature, becomes harmful to aquatic life and causes environmental pollution since it enriches the nutrition of lake and marshes and bays. A simple, quantitative and continuous determination method for ammonia which is suitable for the purpose of on-line measurement is strongly desired.
According to a conventional method, it is possible to determine the concentration of ammonia by distillation-titration methods and colorimetric method. However, these conventional methods are unsatisfactory for the purpose of on-line measurement since the titration method can be performed only manually and the colorimetric method usually requires a complicated filtration process to remove insoluble impurities from a sample solution.
According to another conventional method, ammonia can be determined electrochemically using an ammonia gas-sensitive electrode comprising a combined glass electrode and ammonia gas-permeable membrane. However, this conventional method is also unsatisfactory for on-line measurement since it is necessary to adjust the pH of the sample solution to above 11.0 in order to convert ammonium ions in the sample solution into volatile ammonia gas and this method is affected greatly by impurities such as amines, coexisting in the sample solution and with hydroxides of alkaline earthmetal precipitated from the sample solution under alkaline conditions.
Recently it has been reported that BOD of waste water may be determined with a microbial sensor comprising an oxygen-sensitive electrode and immobilized microorganisms with precision and reproducibility in the following literature references:
I. Karube et al; Biotechnol. Bioeng., 19, 1535 (1977) PA1 I. Karube et al; J. Ferment. Technol., 55, 243 (1977) PA1 K. Matsumoto et al; Anal. Chem. Acta 105, 429 (1979) PA1 M. Hikuma et al; Biotechnol, Bioeng., 21, 1845 (1979).